The most notable part of Musk’s post is this description: “The Model S owner was nonetheless able to exit the highway as instructed by the onboard alert system, bring the car to a stop and depart the vehicle without injury.”

Musk notes that the car struck a large metal object, which pierced the car with 25 tons of force and left a 3-inch-diameter hole in the 1/4-inch armor plate beneath the vehicle. The impact caused a fire in the lithium-ion battery.

Internal firewalls in the battery pack contained the fire to the front of the car, while vents in the battery allowed smoke and flames to leave the car.